This invention relates to an electrically powered pump for pumping liquid by driving a rotor or a plurality of impellers in a pump casing with a motor.
In a traditional electrically powered pump employable for a fuel pump of an automobile as shown in FIG. 1, a rotary shaft 7 of an armature 6 is rotatably fitted to two bearings 5 in a casing 4 which is provided with a field core (a permanent magnet) 2 of a motor 1 and a yoke 3. A pump means 12 is provided in the casing 4 in such a manner that two plates 8 and 9 and a spacer 10 are threadedly secured by a screw 11 across a pump casing. A rotor 14 and a roller 13 are received in the pump casing of the pump means 12. The rotor 14 is fitted to one end of the extension of the rotary shaft 7 from the bearing 5 by means of a woodruff key 15. The axis of the rotor 14 is eccentric to the axis of the pump casing and the roller 13 is adapted to rotate in sliding contact with the inner circumference of the pump casing through the rotation of the rotor 14 driven by the motor 1. In this case, the clearances between the plates 8 and 9 and the rotor 14 are generally required to be set to an extremely minimum, say, about 10.mu.m in order to obtain a necessary pumping performance. In the arrangement where the rotor 14 is secured to the rotary shaft 7 of the armature 6, the axis of the rotary shaft 7 must be substantially perpendicular to the surface of the rotor 14 and the surfaces of the plates 8 and 9 must be substanially parallel to the surface of the rotor 14. Accordingly, every part of the pump means requires manufacture with a fairly high degree of accuracy.
However, it is to be noted that the manufacturing accuracy of the parts is limited and if the manufacturing accuracy is not assured, the preformance and the durability of the pump are reduced, thereby requiring considerable time and labor to the extent that the productivity of the pump is greatly decreased.
In another traditional electrically powered pump 101 employable for a fuel pump of an automobile as shown in FIG. 3, which is a vane type pump wherein a rotor 105 and a roller 106 are provided in a pump housing having plates 102 and 103 and a spacer 104. In this case, the clearances between the plates 102 and 103 and the rotor 105 are generally required to be set to an extremely minimum distance, say, about 10.mu.m so as to obtain a necessary pumping performance. In the arrangement where the rotor 105 is secured to the rotary shaft 108 of the armature 107, the axis of the rotary shaft 108 must be substantially completely perpendicular to the surface of the rotor 105 and the clearance between the rotor 105 and the plate 103 must be set to about 10.mu.m. Accordingly, every pump-related part requires finishing and assembly to an extremely high degree of accuracy, providing for any possible modification in the accuracy after assembling.
In the traditional pump as shown in FIG. 3, the plate 103 is secured to a yoke YO attached to a magnet 109, and the plate 102 is threadedly secured to the plate 103 by means of a screw S, while adjusting the rotary shaft 108 and the rotor 105 to be at right angles.
Because of the high degree of accuracy required during assembling, such a pump is disadvantageous in that the pump plate 102 and the casing CA, or the pump plate 103 and the yoke YO are difficult to construct integrally and the number of parts is increased, whereby the pump itself tends to be larger.
As the sucked fuel is pumped out toward the left as viewed in FIG. 3 under high pressure, such as, about 3 kg/cm.sup.2, the pump must be designed in such a manner that the highly pressurized fuel does not leak out of the pump. For this reason, the casing CA of the pump 101 is so designed as to include a pump housing, a yoke YO, an union UN and a member RE on the discharge side. Further, an oil seal OS is provided around the member RE for preventing leakage of liquid, and the left end of the casing CA is staked, as at k. Accordingly, in this pump structure, the axial length of the pump becomes long and the number of associated parts is increased, thereby leading to increased manufacturing costs.
In a traditional high pressure pump (1.5kg/cm.sup.2 and more), a displacement pump such as a vane pump is employed for a fuel pump of an automobile. Such a pump has a disadvantage that a pulsing motion is created during the pumping operation, thereby causing fuel lines to vibrate and associated noises to be generated. This is especially true a vane pump which disadvantageously creates such noises during operation.
It has been attempted in the prior art to develop a pump, other than such a displacement pump, which is compact and capable of generating a high pressure efficiently. In a regenerative pump substituted for such a displacement pump, and particularly in a regenerative pump having one stage of impeller as seen in FIG. 5, illustrating the corelation of discharge amount and discharge pressure, the flow rate under lower pressure is high, but as the pressure increases, the flow rate greatly decreases, making it diffuicult to ensure proper flow rate under a higher pressure (1.5 kg/cm.sup.2 and more). For this reason, this construction is not applicable to a high pressure fuel pump for an automobile. In another type of regenerative pump having two stages of impeller the flow rate increases under higher pressure and a high cut-off pressure can be obtained. However, generally in the structure of such a regenerative pump, since the clearnaces between both side surface of the impeller and the casing have to be set to an extremely small width, say, about 10-20.mu.m, and the machining accuracy of pump elements must be designed to several .mu.m of tolerance, even in the case of the regenerative pump having one stage of impeller as well as the assembling, accuracy of each part has to be extremely critical. Furthermore, the right angle of the armature rotary shaft against the impeller coaxially fitted to the rotary shaft is critically ensured in association with the clearances of about 10-20.mu.m between both side surfaces of the impeller and the casing. This casuses reduced productivity of such pumps. Particularly in a regenerative pump having two stages of impeller, because of the abovementioned requirements, the productivity of such pumps is further decreased to the extent that such pumps are not applicable for a high pressure use such as in a fuel pump of an automobile.